Alternators are used to convert mechanical energy from a vehicle engine into electrical energy for the vehicle. The electrical energy produced by the alternator is used to charge the vehicle battery, and may also be used to power electric loads on the vehicle.
The alternator generally includes a rotatable field coil positioned within a stator having a plurality of stator windings. Operation of the engine results in rotation of the field coil. Current flowing through the rotating field coil provides a rotating magnetic field. This rotating magnetic field induces an AC output voltage in the stator windings. The AC voltage in the stator windings is rectified and delivered to the vehicle battery and/or electric loads on the vehicle.
Modern vehicle alternators include a regulator that controls the current through the field coil. In general, when more current is provided to the field coil, the output voltage of the alternator increases. When less current is provided to the field coil, the output voltage of the alternator decreases.
The modern motor vehicle engine compartment is increasingly cramped as manufacturers strive to reduce the size of vehicles, including the engine compartment. With multiple components packed in a relatively small space, the heat generated by multiple components increases the temperature within the engine compartment. Furthermore, the tightly packet engine compartment reduces the space available for cooling air to flow through the engine compartment and reduce component temperatures. Excessive engine compartment temperatures may adversely affect the performance of the components positioned in the engine compartment, including the alternator. Thus, as underhood temperatures continue to increase, new methods of reducing heat sources in the engine compartment are sought.
Vehicle alternators have traditionally utilized fixed frequency field drivers. In these alternators, a field driver circuit provides pulses of current to the field coil at a fixed frequency. However, this field driver circuit is one of the main sources of heat generated within the alternator. The heat generated by the field driver circuit is further intensified by the switching action of the field driver circuit. Because the field driver circuit is a significant source of heat, it would be advantageous to reduce the heat generated by the field driver circuit, and thus reducing the heat within the engine compartment.
In addition to the generation of heat, alternator switching may also result in magnetic noise. Magnetic noise may have adverse affects for the vehicle, including reduced efficiency of the alternator and audible noise. Thus, methods of reducing magnetic noise in an alternator are also desired.